Evaluation of the effects of three different rapid maxillary expansion appliances on craniofacial structures with finite element analysis

The aim of this study is to evaluate the craniofacial and dentoalveolar effects of the hyrax, fan type and double hinged expansion screws used for rapid maxillary expansion by using three dimensional finite element method. The construction of the three-dimensional finite element model was based on computer tomography scans of a 12 year old patient who needs maxillary expansion. These models consisted of approximately 1800000 tetrahedral element with 2750000 nodes. The Von Mises stress distribution following 0.2 mm of expansion and displacement distributions following 5 mm of expansion were evaluated. The highest stresses accumulation was observed in the sutura zygomaticomaxillaris area with all three appliances. An increase of stress was noticed at the pterygomaxillary fissure, medial and lateral pterygoid plates of the sphenoid bone and the nasal areas. When all the anatomical structures were evaluated overall, the stress distributions were found highest with the hyrax expansion screw and the lowest values were recorded with the fan type expansion screw. The wedge-shaped opening was observed with all three appliances. In the transverse plane, the maximum posterior expansion was achieved with hyrax appliance, while the maximum anterior expansion was observed with double-hinged appliance. Maxilla moved downward and forward with all three appliances. The higher amount of downward displacement of the maxilla was recorded with the hyrax appliance. On the other hand, forward maxillary displacement amount is higher with the double hinged appliance. Maxilla rotated posteriorly with the hyrax and fan type appliances, while parallel movement occurred with the double hinged appliance. Dentoalveolar complex moved posteriorly with hyrax appliance while anterior displacement was recorded with fan type and double-hinged appliances. When all the anatomical structures were evaluated in the vertical plane, a tendency in inferior displacement was recorded with hyrax appliance.